The present invention relates to a method for towing a vehicle equipped with an automatic manual transmission (AMT). In particular, an aspect of the invention will find its application in connection with automotive vehicles with an AMT where a lubricating system arranged in the AMT for lubricating said AMT is driven by a propulsion unit of the vehicle during idle drive.
An aspect of the invention also relates to a device intended for such a method for towing a vehicle equipped with an AMT.
An aspect of the present invention also relates to a computer program and computer program product both to be used with a computer for executing said method.
Automated manual transmissions (AMT) have become increasingly common in heavy-duty vehicles as microcomputer technology has developed further and made it possible, with a control computer and a number of actuators, for example servo motors, to precision-regulate engine speed, engagement and disengagement of an automated disk clutch between the engine and the gearbox and also the coupling means of the gearbox in relation to one another, so that soft shifting is always obtained at the correct engine speed. In heavy-duty vehicles, these automatic gearboxes are often equipped with a basic gearbox, which has forward and reverse gears, and also auxiliary gears, which auxiliary gears can be arranged in series before and/or after the basic gearbox. An example of an auxiliary gear arranged serially before the basic gearbox is a split gear and of an auxiliary gear arranged serially after the basic gearbox is a range gear (see, for example, WO0192049).
In order to introduce power shifting possibilities in an AMT the dual clutch transmissions (DCT) have been developed. This is basically an AMT with dual input shafts and corresponding clutches. A known example of a DCT is shown in US2005/0204841 and U.S. Pat. No. 4,777,837.
Common for both of the above mentioned types of transmissions is that there is often used a so-called forced-feed lubricating oil system in order to increase the service life of transmissions, when for example used in heavy trucks and buses. Such a forced-feed lubricating oil system usually comprises an oil pump which among other things supplies bearings in the transmission with an oil flow for lubrication and cooling. The oil pump may be located in various ways but usually it is driven directly or indirectly by an intermediate shaft in the transmission. The intermediate shaft is drivingly connected to a vehicle propulsion unit through an input shaft of the transmission. Driven wheels of the vehicle are drivingly connected to the intermediate shaft through an output shaft of the transmission. The input shaft, the intermediate shaft and the output shaft can have several different gears arranged to drivingly engage or disengage said input shaft to said intermediate shaft, and to drivingly engage or disengage said intermediate shaft to said output shaft. The engagement and disengagement of the different gears is controlled by a control unit.
When the vehicle is driven, the propulsion unit drives the forced-feed lubricating oil system by rotation of the intermediate shaft. During idle drive, that is when the vehicle is stopped and the propulsion unit is running, all gears between the intermediate shaft and the output shaft are disengaged and a gear between the input shaft and the intermediate shaft is engaged in order to drive the forced-feed lubricating oil system and secure lubrication during idle drive of the vehicle.
If the vehicle has to be towed away with the propulsion unit stopped the forced-feed lubricating oil system will not he driven and there is a risk of severe transmission damage since gears and bearings in the transmission are running without lubrication during towing. A known solution is to disconnect the driven wheels from the output shaft by demounting a propeller shaft of the vehicle.
A technical problem is to provide an alternative and improved solution to not risk damaging an AMT during towing of the vehicle.
It is desirable to provide an improved method and device for securing lubrication of an AMT in a vehicle during towing.
The method according to an aspect of the invention is a method for securing lubrication of an automated manual transmission in a vehicle, when towing said vehicle, and where a transmission lubrication system is drivingly connected to and driven by rotation of an intermediate shaft of said automated manual transmission. Said method is characterized by the following steps executed in mentioned order:                registering a signal that towing of the vehicle is demanded,        disengaging all gears that are arranged to drivingly engage or disengage an input shaft to said intermediate shaft of said automated manual transmission, and engaging one gear that is arranged to drivingly engage or disengage said intermediate shaft to an output shaft of said automated manual transmission.        
According to one embodiment of the method according to an aspect of the invention said signal is manually initiated.
According to another embodiment of the method according to an aspect of the invention, said signal is automatically initiated when a vehicle fault is registered that will make towing of the vehicle necessary.
According to a further embodiment of the method according to an aspect of the invention, said signal is automatically initiated when vehicle velocity other than zero is registered and that a propulsion unit of said vehicle is turned off.
The device according to the an aspect of invention is an AMT in a vehicle comprising an input shaft, an intermediate shaft and an output shaft with several different gears arranged to drivingly engage or disengage said input shaft to said intermediate shaft, and to drivingly engage or disengage said intermediate shaft to said output shaft, and where a transmission lubrication system is drivingly connected to and driven by rotation of said intermediate shaft. The device is characterized in that a control unit is arranged to disengage all said gears drivingly connecting said input shaft and said intermediate shaft and to engage one of said gears arranged to drivingly connect said intermediate shaft and said output shaft, upon registration of a signal that towing of the vehicle is demanded and in order to drivingly connect said lubrication system with driven wheels of the vehicle.
According to one embodiment of the device according to the an aspect of invention said signal is initiated through a control for manually initiating said signal.
According to another embodiment of the device according to an aspect of the invention said AMT further comprises an auxiliary gearing connected in series to said output shaft and where an auxiliary gearing output shaft is further connected to said driven wheels. The auxiliary gear can for example be a range gear. Such a device is then further characterized in that said control unit is arranged to engage a gear of said auxiliary gear in order to drivingly connect said output shaft with said auxiliary gearing output shaft, upon registration of a signal that towing of the vehicle is demanded and in order to drivingly connect said lubrication system with driven wheels of the vehicle.